feat: add workflow for generating changelog preview as PR comment

.github/workflows/changelog-preview-comment.yml

@@ -0,0 +1,47 @@
+name: Generate changelog preview
+
+on:
+  workflow_call:
+    inputs:
+      cliff_config_url:
+        type: string
+        description: URL to a git-cliff configuration file
+        default: https://raw.githubusercontent.com/holochain/release-integration/refs/heads/main/pre-1.0-cliff.toml
+
+jobs:
+  changelog-preview-comment:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout PR commits only
+        uses: actions/checkout@v4
+        with:
+          ref: ${{ github.event.pull_request.head.ref }}
+          fetch-depth: ${{ github.event.pull_request.commits }}
+          sparse-checkout: ''
+          sparse-checkout-cone-mode: false
+
+      - name: Checkout all tags
+        run: git fetch --tags
+
+      - name: Install git-cliff
+        uses: taiki-e/install-action@v2
+        with:
+          tool: git-cliff@2.9.1
+
+      - name: Run git cliff
+        run: |
+          git cliff \
+            --bump \
+            --config-url="${{ inputs.cliff_config_url }}" \
+            --strip=all \
+            --output=PR_CHANGELOG.md
+
+      - name: Add changelog preview as comment
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          gh pr comment ${{ github.event.pull_request.html_url }} \
+            --body="$(printf 'The following will be added to the changelog\n\n---\n\n'; cat PR_CHANGELOG.md)" \
+            --edit-last \
+            --create-if-none